1. Field of the Invention
The present invention relates to a sheet feeding apparatus, and more particularly, to a sheet feeding apparatus for a printing device to pick up sheets from a tray and deliver the sheets into a printing device sheet by sheet.
2. Description of the Related Art
A printing device 100, such as a copying machine, includes a sheet feeding apparatus having a tray 11 for loading sheets S to be supplied into a printing device 10 and a pickup roller 12 introducing the sheets S on the tray 11 into a sheet feeding path (not shown) of the printing device 10 sheet by sheet as shown in FIGS. 1 and 2. The sheet feeding apparatus is used for feeding both sheets and documents. As an automatic document feeding (ADF) type printing device is known to automatically feed the documents, which are to be duplicated, as well as the sheets onto which images are printed, the sheet feeding apparatus has been applied to the printing device not only feeding the sheets but also feeding the documents.
Referring to FIG. 2, when a motor 13 rotates the pickup roller 12, an uppermost sheet S stacked on the tray 11, which is in contact with the pickup roller 12, is inserted into the printing apparatus 10. The sheet feeding apparatus includes a cover 14 that is closed during a printing process to protect the pickup roller 12 and an inlet of the printing device 10, into which the sheets S are inserted as shown in FIG. 2.
In order to smoothly feed the sheets S into the printing device 10, the pickup roller 12 must hold front ends of the sheets S disposed under the pickup roller 12. When an excessive amount of sheets S is loaded on the tray 11, it is difficult for the pickup roller 12 to hold the sheets S. Therefore, the amount of the sheets S that can be loaded on the tray 11 at one time is limited to about 20 sheets. Consequently, a user has to repeat to load the sheets S on the tray 11 to print a large amount of documents. In addition, according to the constitution of the sheet feeding apparatus as shown in FIGS. 1 and 2, an inclination of the tray 11 is angled as steep as possible toward the pickup roller 12 to smoothly slide the sheets S disposed under the pickup roller 12. However, the constitution of the sheet feeding apparatus increases a height of the printing device 10, so that the printing device 10 occupies a large space. In addition, according to the above constitution of the sheet feeding apparatus, more than two sheets may slide under the pickup roller 12, which is referred to as double feeding of the sheets S.